For logistical reasons, I measured a different sample of the HiFi Rose RA180—serial number ESL203AB000182—from the one auditioned by Julie Mullins. I performed the measurements with my Audio Precision SYS2722 system,1 examining the amplifier’s performance in both normal mode and in bridged (“BTL”) mode, following the instructions in the excellent manual. As Julie Mullins found, the RA180 doesn’t recognize 5G Wi-Fi networks, but I was able to connect it to my Netgear NightHawk router’s 2.4GHz network. I could control the RA180 with the RoseAMPConnect app on my iPhone, as well as with the remote control and the front-panel controls.
As the RA180’s output stages operate in class-D, all the measurements other than frequency and RIAA responses were taken with Audio Precision’s auxiliary AUX-0025 passive low-pass filter, which reduces the level of noise above 80kHz and eliminates noise above 200kHz. Without the filter, in normal mode, a very high 1.33V of ultrasonic noise was present at each pair of loudspeaker terminals, with a center frequency of 525kHz. The ultrasonic noise level rose to 1.6V in bridged mode. In both
